Spectrum-efficient user association in caching enabled dense small cell network

In this paper, we reveal the fundamental limitation of network densification on the performance of caching enabled small cell network (CSCN) under two typical user association rules, namely, content- and distance-based rules. It indicates that immoderately caching content would significantly change the interference distribution in CSCN, which may degrade the network area spectral efficiency (ASE). Meanwhile, it is shown that content-based rule outperforms the distance-based rule in terms of network ASE only when small cell base stations (BSs) are sparsely deployed with low decoding thresholds. Moreover, it is proved that network ASE under distance-based user association serves as the upper bound of that under content-based rule in dense BS regime. To enable more spectrum-efficient user association in dense CSCN, we further optimize network ASE by designing a probabilistic content retrieving strategy based on distance-based rule. With the optimized retrieving probability, network ASE could be substantially enhanced and even increase with the growing BS density in dense BS regime.